A. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits.
B. Description of the Related Art
When manufacturing integrated circuits, deposition processes are employed to deposit thin layers of insulative material and conductive material onto wafers. Deposition has been performed through various well known processes, such as chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) and physical vapor deposition (xe2x80x9cPVDxe2x80x9d or xe2x80x9csputteringxe2x80x9d).
In a CVD process, a wafer is loaded into a chemical vapor deposition chamber. Conventional CVD processes supply reactive gases to the wafer surface where heat-induced chemical reactions take place to form a thin film layer over the surface of the wafer being processed. One particular CVD application is the deposition of a titanium containing compound, such as titanium nitride, over a wafer from a process gas that includes a metallo-organic compound. One such compound is tetrakis(dialkylamido)titanium (Ti(NR2)4) having the following structural formula: 
wherein R at each occurrence independently is in an alkyl group, of, for example, 1-5 carbon atoms. For example, it is common to use tetrakis(dimethylamido)titanium (TDMAT), which has the formula Ti(N(CH3)2)4.
A carrier gas, such as helium, argon, nitrogen, or hydrogen brings the compound into the chamber, so that it may be infused with energy. The energy may be generated through a thermal heat source, in the case of thermal CVD, or a radio frequency (xe2x80x9crfxe2x80x9d) signal source, in the case of plasma enhanced CVD. The energized chemical vapor reacts with the wafer""s surface to form a thin layer of material on the wafer. When the TDMAT chemical vapor is used, a titanium nitride film is deposited on the wafer""s surface.
In a sputtering process, a wafer is placed in a physical vapor deposition (xe2x80x9cPVDxe2x80x9d) chamber, and the chamber is filled with a gas, such as argon. A plasma containing positively charged ions is generated from the gas, by creating an electrical field in the chamber. The positively charged ions accelerate and collide into a target material, which is mounted in the chamber. Atoms of the target material are thereby separated from the target and deposited on the wafer to form a layer of target material on the surface of the wafer.
In a traditional sputtering process, the bombardment of the target material by the positively charged ions is enhanced by providing a negative bias to the target material. This is achieved by providing a radio frequency signal to an electrode that supports the target material.
A separate rf signal may be inductively coupled to the chamber for generating positively charged ions in a high density plasma PVD chamber. A high density plasma PVD chamber may include another rf signal coupled to a wafer support for improving the attraction of the target material to the wafer.
A deposition chamber, such as a CVD chamber or a PVD chamber, may be used to deposit diffusion barriers in an integrated circuit. Diffusion barriers inhibit the diffusion of a contact metal, such as aluminum and copper, into the active region of a semiconductor device that is built on a silicon substrate. This prevents the interdiffusion of a contact metal into the substrate. Unlike an insulative layer of material, a diffusion barrier forms a conductive path through which current may flow. For example, a diffusion barrier may be employed to overlie a silicon substrate at the base of a contact hole.
A severe interdiffusion between a contact metal and a silicon substrate can begin to take place when the integrated circuit is heated to temperatures in excess of 450xc2x0 C. If an interdiffusion is allowed to occur, the contact metal penetrates into the silicon substrate. This causes an open contact in the integrated circuit and renders the integrated circuit defective.
In the fabrication of integrated circuits, there has been an increased use of aluminum and copper metalization processes operating at high temperatures, in excess of 450xc2x0 C. Therefore, it desirable to have diffusion barriers with a greater ability to inhibit the diffusion of contact metals, such as aluminum and copper.
Traditionally, diffusion barriers have been made thicker to accommodate such a desire. However, smaller geometries are being employed in the fabrication of integrated circuits. The smaller geometries decrease the dimensions of contact holes, thereby making it desirable for diffusion barriers to become thinner and more conformal.
FIG. 1 illustrates a diffusion barrier 100 that resides between a conductive region 105 of a silicon substrate 101 and a contact plug 102. A contact hole 103 is formed in an insulative layer of material 104, such as silicon dioxide, which overlies the substrate 101. The diffusion barrier 100 is ideally formed so that it is thin and substantially conforms to the contours of the surface of the contact hole 103.
If the diffusion barrier 100 is thin and highly conformal, the contact metal 102 is able to. form a sufficiently conductive ohmic contact with the silicon substrate""s conductive region 105. If the diffusion barrier 100 is too thick or poorly formed, as shown in FIG. 2, it will prevent the contact metal 102 from forming a sufficiently conductive ohmic contact with the substrate region 105.
In FIG. 2, the poorly formed diffusion barrier 100 severely narrows the opening of the contact hole 103. The narrow opening causes the contact metal 102 to form so that it does not reach the base of the contact hole 103. As a result, a void 106 is formed.
In order to ensure a good ohmic contact between the contact metal 102 and the substrate region 105, it is desirable for the resistance of the diffusion barrier 100 to be minimal. Typically, a resistivity value of 1,000 xcexcxcexa9-cm or less is acceptable. One material that has been successfully employed as a diffusion barrier is titanium nitride (TiN).
However, some deposition processes, such as those using TDMAT, provide an unstable barrier layer having high resistivity. In the case of TDMAT, this is partly due to a significant fraction of the deposited barrier material being composed of a carbon (hydrocarbons, carbides, etc.). Further, the titanium, a chemically reactive metal, may not be completely reacted in the film. It would be desirable to treat such a layer of barrier material with a post-deposition processing, so that its resistivity is reduced and stabilized.
In manufacturing an integrated circuit, it is desirable to perform successive steps of the manufacturing process, such as deposition and post-deposition processing, in the same chamber (xe2x80x9cin-situxe2x80x9d). In-situ operations reduce the amount of contamination that a wafer is exposed to by decreasing the number of times that the wafer is required to be transferred between different pieces of manufacturing equipment. In-situ operations also lead to a reduction in the number of expensive pieces of manufacturing equipment that an integrated circuit manufacturer must purchase and maintain.
Accordingly, it would be desirable to construct a highly conformal thin diffusion barrier with an increased ability to inhibit the diffusion of contact metals, such as aluminum or copper. Additionally, it is desirable for such a diffusion barrier to have a resistance that allows the diffusion barrier to form a good path for current flow. It would also be desirable to construct such a diffusion barrier in-situ.
An apparatus and method in accordance with the present invention provides for carrying out the in-situ construction of a highly conformal diffusion barrier with improved resistivity. By practicing aspects of the present invention, the diffusion barrier""s ability to impede the diffusion of contact metals, such as aluminum or copper, may be enhanced. Such an enhancement of the diffusion barrier will not significantly enlarge its thickness or resistivity beyond acceptable limits.
A semiconductor processing apparatus, which enables practicing embodiments of the present invention, may include a processing chamber, showerhead, wafer support, and rf signal means. In one embodiment of the present invention, the semiconductor wafer processing apparatus is capable of performing chemical vapor deposition.
The showerhead is adapted to supply gases in the processing chamber. The wafer support provides for supporting a wafer in the processing chamber. The rf signal means may be coupled to both the showerhead and the wafer support for providing a first rf signal to the showerhead and a second rf signal to the wafer support. Alternatively, the rf signal means may only be coupled to provide a rf signal to the wafer support.
The wafer support is supported in the processing chamber by a support arm. The support arm couples the rf signal means to the wafer support. The support arm also couples a thermocouple housed in the wafer support to a temperature determination device for measuring the temperature of the wafer support. The thermocouple is electrically isolated from the rf signal means.
When practicing an aspect of the present invention, a film may be constructed on a wafer. First, a layer of material is deposited on the wafer. The material may be a binary metal nitride MxNy or a ternary metal silicon nitride MxSiyNz (where M may be titanium Ti, Zirconium Zr, hafnium Hf, tantalum Ta, Molybdenum Mo, Tungsten W, and other metals). The deposition of the material may be carried out by a variety of means, such as chemical vapor deposition and physical vapor deposition.
After the material is deposited, the material is plasma annealed, so as to reduce the resistivity of the layer of material. The plasma annealing may include an exposure of the material to an environment containing ions and electrically biasing the layer of the material to cause the ions to impact the material.
Alternatively, the annealing may consist of multiple annealing steps that are performed sequentially with different gases. For example, a first annealing step may employ a mixture of nitrogen and hydrogen, while a subsequent annealing step uses a mixture of nitrogen and helium. The subsequent annealing step removes hydrogen molecules from the material to reduce its resistivity.
Once the annealing is completed, the layer of material may be oxidized. The oxidation enhances the material""s ability to inhibit the diffusion of contact metals, such as aluminum. Alternatively, the annealed layer of material may be exposed to a silane gas to enhance the material""s ability to inhibit the diffusion of contact metals, such as copper.
In accordance with the present invention, the deposition, annealing, and either oxidation or silane exposure may all be performed in a single chamber, without need for removing the wafer from the chamber before all three operations are completed. Accordingly, the deposition, annealing and either oxidation or silane exposure of the material may be performed in-situ.